Feature #11049: Enumerable#grep_v (inversed grep)

• Status: Closed
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -

[sorah (Sorah Fukumori)]

sometime I want to do grep -v like operation:

%w(aaa bbb ccc).reject { |x| /b/ === x } #=> ["aaa", "ccc"]

We already have Enumerable#grep, so I propose to add Enumerable#grep_v.

%w(aaa bbb ccc).grep(/b/) #=> ["bbb"]
%w(aaa bbb ccc).grep_v(/b/) #=> ["aaa", "ccc"]

Naming / Interface

This idea is mentioned at DevelopersMeeting20150408Japan by me. Matz has said "I don't disagree for the feature. So this remains naming (interface) problem."

I'm not sure grep_v is the best name for this feature; feedback are welcomed.

Ideas

• grep_v(pattern) (the first patch)
• grep(pattern, inverse: true)
• grep!(pattern)

[recursive-madman (Recursive Madman)]

How about implementing Regexp#invert instead?

  /b/.invert #=> /[^(?:b)]/

Like this for example:

class Regexp
  def invert
    self.class.new("[^(?:#{source})]")
  end
end

%w(aaa bbb ccc).grep(/b/) #=> ["bbb"]
%w(aaa bbb ccc).grep(/b/.invert) #=> ["aaa", "ccc"]

[Eregon (Benoit Daloze)]

Recursive Madman wrote:

How about implementing Regexp#invert instead?

Like this for example:

class Regexp
  def invert
    self.class.new("[^(?:#{source})]")
  end
end

That only works for some regexps, I doubt there is a proper and well defined inverted regexp for any Regexp.

[Eregon (Benoit Daloze)]

grep(pattern, inverse: true) seems the least surprising to me.
But of course it does not buy much compared to #reject.

[recursive-madman (Recursive Madman)]

Benoit Daloze wrote:

That only works for some regexps, I doubt there is a proper and well defined inverted regexp for any Regexp.

Could you provide an example that doesn't work?

[akr (Akira Tanaka)]

Recursive Madman wrote:

Benoit Daloze wrote:

That only works for some regexps, I doubt there is a proper and well defined inverted regexp for any Regexp.

Could you provide an example that doesn't work?

class Regexp
  def invert
    self.class.new("[^(?:#{source})]")
  end
end

%w(aaa bbb ccc).grep(/abc/) #=> []
%w(aaa bbb ccc).grep(/abc/.invert) #=> []

[nobu (Nobuyoshi Nakada)]

invert looks same as my proposal, Regexp#!.

[sawa (Tsuyoshi Sawada)]

How is this proposal different from #9602? I thought that Matz had already suggested to modify select, and Sam Rawlins had implemented select and reject.

[sorah (Sorah Fukumori)]

• Assignee set to matz (Yukihiro Matsumoto)

I didn't know/hear that.

@matz (Yukihiro Matsumoto) what do you think for now?

[akr (Akira Tanaka)]

• Related to Feature #5588: add negation flag (v) to Regexp added

[akr (Akira Tanaka)]

• Related to Feature #9602: Logic with `Enumerable#grep` added

[haraldb (Harald Böttiger)]

Recursive Madman wrote:

How about implementing Regexp#invert instead?

As grep using the case statement this would be ignoring a lot of cases that would be handy:

array.invert_grep(Array) # Select all elements that are not arrays.

[matz (Yukihiro Matsumoto)]

grep_v seems OK. Accepted.

Matz.

[sorah (Sorah Fukumori)]

• Status changed from Open to Closed

Thanks, committed at r50491, r50492.

[shyouhei (Shyouhei Urabe)]

• Related to Feature #8921: Allow select, reject, etc to accept a regex added